1. Field of the Invention
This invention relates to a method of manufacturing an olefinic oxide from an olefin and oxygen.
Although ethylene can be oxidized to ethylene oxide at elevated temperatures in the presence of a silver catalyst, the yields of olefinic oxide from higher olefins are low.
2. Prior Art
Several indirect but more selective methods of oxidizing olefins have therefore been developed, two of which are believed to be currently in use, viz:
1. In the chlorohydrin process (U.S. Pat. No. 3,277,189), olefin is reacted with chlorine in the presence of water to give olefin chlorohydrin, which is further reacted with base to give the olefinic oxide. The disadvantage of this process is that inorganic chlorides and hydrogen chloride are also produced. Various ways of utilizing the inorganic chlorides have been proposed (for example as described in British Patent Specification No. 1,425,022) but even this process has the disadvantage of the high cost of electrical energy and cell inefficiencies.
2. In another process, more particularly described in U.S. Pat. No. 3,360,584, propylene oxide is produced in 80% yield by reaction of propylene with tertiary butyl hydroperoxide, itself produced by liquid phase oxidation of i-butane. Although a high yield is obtained, capital costs are high since the process is multistage, a complex distillation is involved in product separation and the economics are affected by the market price for the by-products, t-butanol or i-butene. Byproduct recycle is possible but consumes hydrogen.
In a proposed process, more particularly described in U.S. Pat. No. 3,806,467, olefins are oxidized by a catalytic reaction with hydrogen peroxide. This process suffers from the disadvantage that the use of hydrogen peroxide as oxidizing agent leads either to high capital costs for the process, as with the organic hydroperoxide route, or high chemical costs since it is expensive to produce by current industrial processes, and needs to be concentrated if used as an aqueous solution.
Several processes have been proposed for the direct liquid phase epoxidation of olefins higher than ethylene, e.g. U.S. Pat. Nos. 3,856,826 and 3,856,827 and Erdoel Kohle 25 584 (72). These processes involve contacting the olefin, dissolved in a suitable solvent, with oxygen at elevated temperature and pressure, in the presence of a catalyst, usually an organic complex of molybdenum. However, selectivity for the olefin oxide is at best 50-60% in these processes, even at low conversions.
British Pat. No. 1,206,166 discloses a method for catalyzing the reaction of oxygen with olefins in the liquid phase using as catalyst a complex of a Group 8 metal capable of reversibly forming an adduct with oxygen. In particular, Ir (P Ph.sub.3).sub.2 CO Cl, Rh (P Ph.sub.3).sub.3 I and Rh (P Ph.sub.3).sub.3 Cl are used as catalysts. No examples are given for olefins lower than C.sub.6, for which the selectivity is only 26%.
Other published work gives results for the dioxygen complexes (P Ph.sub.3).sub.2 MO.sub.2 (M=Pd or Pt) which used as olefin epoxidation catalysts. According to one source (J. Organometallic Chem. 26 417 (71)), the platinum complex does catalyze the oxidation of cyclohexene by initiating a free radical reaction, thus accounting for a distribution of products and a low selectivity to the epoxide of 1-3%. R. Sheldon and J. Van Doorn (J. Organometallic Chem. 94 115 (75)) find that there is no direct reaction between these two complexes and simple olefins such as cyclohexene at 60.degree. C.